Page 103 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1

Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)

Theory of Non-Aqueous Titrations

• The acidity of weak acids can be enhanced in presence of a basic solvent, this is

because basic solvent has a higher affinity to take up protons from the acid.

• So, acetic acid behaves as a strong acid in ammonia solution (basic solvent).

• Also, the basicity of weak bases can be enhanced in presence of acidic solvent.

• This is called the leveling effect of the solvent.

• By using this concept, the strength of weak acidic or weak basic drugs can be

enhanced by dissolving in the appropriate solvent to enhance its strength and then can

be titrated by acid-base titration (non aqueous titration).

Types of solvents in non aqueous titrations:

These are acidic solvents and are used to enhance the
1) Protogenic solvents
basicity of weak bases.
yield protons (Acidic)
Examples: glacial acetic acid.

These are basic solvents and are used to enhance the
2) Protophilic solvents:
acidity of weak acids.
can accept protons (Basic)
Examples: pyridine, ethylenediamine and

dimethylformamide (DMF).

3) Amphoteric solvents: These solvents behave as acid as well as base

can accept or yield protons depending on the substance dissolved in it.

(acids or bases) Examples: alcohol.

4) Aprotic solvents: They are used in dissolving the drugs especially those

neither accept proton nor which are insoluble in water.

donate proton. Examples: benzene, carbon tetrachloride.

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